A conventional damper for supporting a mechanical chassis of an optical disk unit and so on is a push-type damper comprising one type of elastic body having an E value of 1.0.times.10.sup.4 kg/cm.sup.2 or less as shown in FIG. 5 or 6. Usually, a damper is generally used which comprises an elastic body holding a rotary part or drive means 8 of a rotating component such as a medium disk 3 and a mechanical chassis 2 mounting an optical transmitter or optical receiver (hereinafter referred to as optical pickup 4) on the face side and fixing them to a box 5 with a screw 6 or the like as shown in FIG. 7.
The conventional push type damper comprising one type of elastic body has a shape shown in FIG. 5 or 6, and the ratio between spring constants in the directions vertical to and parallel with the plane of the disk 3 ranges between approx. 0.5 and 2 times, even if spring constants are changed.
Conventionally, the characteristic requested for a damper is to provide an effect of the reduction of transmissibility of vibration acceleration by suppressing vibration so that the relative distance between the disk 3 and the optical pickup 4 can be kept constant, specifically by keeping the natural frequency due to the damper at the square root of 0.5 or less at a purposed frequency and therefore a spring constant to the total weight of the mechanical chassis 2, disk 3, and optical pickup 4 is obtained.
However, the rotating disk 3 produces vibration in the direction vertical to the rotation axis due to weight imbalance caused by a dimensional tolerance, machining error or the like, namely in the direction parallel with the disk. Unless the damper has only a low elasticity to the vibration, the mechanical chassis itself greatly vibrates. To stop the vibration, it is necessary to control the vibration with a force larger than the angular moment due to the weight imbalance. To control the vibration, it is preferable to use a method of fixing the mechanical chassis to the box or base 5. However, if the ratio between spring constants of the damper in the directions vertical to and parallel with the plane of the disk 3 takes a range from approx. 0.5 to 2 times, it is impossible to stop the vibration. On the contrary, vibration having a frequency close to the natural frequency of to the damper, that is, resonance occurs and worse result occurs.